Boats, power and sail, with cruising accommodations especially in the 20 to 40 foot range, are not often equipped with built-in air conditioning systems to make cabins comfortable places to eat and sleep dockside in hot, humid summer weather. This invention is directed to providing a unit which solves this problem by (1) through-hatch mounting, so that the unit occupies the minimum of the limited below-deck space, but provides convenient below-deck access to its controls; (2) ready adaptability to the usual range of hatch parameters; (3) easy and tool-free installation and removal, without disconnecting the hatch cover, if hinged; and (4) above-deck location of the mechanisms, in an easily-portable, self-contained, weather-proof assembly.